As in a conventional BGA (Ball Grid Array) and CSP (Chip Scale Package), a semiconductor package component having bumps on the undersurface is mounted according to the process shown in FIGS. 6(A) to 6(D).
In FIG. 6(A), SnAgCu solder paste 601 is printed on second electrodes 104 of a circuit board 105. Subsequently, as shown in FIG. 6(B), bumps 103 formed on first electrodes 102 of a semiconductor package 101 are mounted in contact with the second electrodes 104 through the SnAgCu solder paste 601.
In FIG. 6(C), reflowing is performed. Reflowing melts the SnAgCu solder paste 601 printed on the second electrodes 104 and the solder of the bumps 103 formed on the first electrodes 102, moving the semiconductor package 101 to a proper position by self alignment. After that, the solder at its melting temperature or lower is solidified into solder 602, completing an electrical connection of the semiconductor package 101 to the circuit board 105. At this point, the SnAgCu solder paste 601 printed on the second electrodes 104 has the same composition as the bumps 103 of the semiconductor package 101. Generally, SnAgCu solder is used.
The semiconductor package 101 having the bumps on the undersurface as in a BGA or a CSP is used for mobile devices such as a cellular phone. A function required for such products is drop impact resistance. As a solution, for example, if a BGA and the circuit board 105 are soldered to each other, a technique shown in FIG. 6(D) is used in which an underfill 603 is filled between the semiconductor package 101 and the circuit board 105 after soldering with the SnAgCu solder 602, improving the drop resistance of joints (Patent Literature 1).
In recent years, the use of a SnBi solder material having a lower melting point than conventional SnAgCu solder has been examined in response to growing interest in environmental issues, particularly, global warming. However, the connection reliability of BGA connections using low melting solder has not been ensured.
A conventional BGA connection using low melting solder will be described below.
For example, a mounting structure described in Patent Literature 2 is shown in FIG. 7.
The mounting structure includes a semiconductor package 101 having first electrodes 102, a circuit board 105 having second electrodes 104, bumps 103 formed on the first electrodes 102, bonding members 106, each being disposed between the bump 103 and the second electrode 104 so as to electrically connect the first electrode 102 and the second electrode 104 via the bump 103, and a reinforcing resin 107 disposed around each of the bonding members so as to cover a joint between the bump 103 and the bonding member 106 and the bonding member. Adjacent portions of the reinforcing resin 107 are separated so as to prevent contact with each other.